The present invention concerns a timepiece including a frame upon which is held, in a detachable manner, and with the aid of a particular fixation device, an added element.
Further, this invention concerns a method of assembling such an element on a frame of the type mentioned above.
More particularly, the invention concerns a timepiece and an assembling method, in which the frame is formed of a synthetic material, said added element being made of any material, for example a metal material.
It is also to be noted that in a particular application, the added element may advantageously be formed by a protective plate applied against the frame, and added to the latter in order to protect certain of the fragile components of said timepiece.
In conventional timepieces, such protection plates are held in a detachable manner by screws whose thread is inserted into the synthetic material forming the frame.
This arrangement has numerous disadvantages which detract from the quality and durability of the timepiece.
Further, when the added piece is dismantled and reassembled on the frame, this arrangement can lead to damage of the components by the fixation device.
In timepieces whose frame is formed of a synthetic material, such as for example plastic, the assembly, dismantling and reassembling operations of the added elements, such as protection plates of the type mentioned above, lead to the progressive tearing of the threads formed in the synthetic material. Thus, the number of dismantling/reassembling operations of the plate on the frame must be relatively limited.
Further, given that it is very difficult to measure the tightening forces which are applied when the screw is manually put back in place in the hole which has been tapped by the screw itself in the frame (self-tapping screw), it may happen that this force is markedly greater than the shearing resistance of the threads and, at the time of the first reassembling, this excessive force may ruin the threads and render inoperative the gripping action of the screw against the plate.
It is also to be noted that, during these operations, screws which are very small may be lost by the operator.
Further, as numerous components are arranged in a very compact manner in the timepiece and as certain of them, such as for example the coil, are not necessarily covered by the protective plate, the operator's tool which is level with the plate, may slip when the screw or screws are being put into place and harm, for example, the wires of the coil causing serious damage to the coil.
It is thus clear that this type of fixation is not satisfactory for the detachable assembly of an added element on a frame of a timepiece forming, in particular, a plate made of a synthetic material.
Further, it has been proposed that fixing members functioning with a click mechanism be provided directly on the added element. However, in view of the size of the components concerned, these members present real manufacturing difficulties and their operation is uncertain, because of the low margins required for the operation of this type of device and the difficulties in ensuring such low margins in the manufacturing of frames in synthetic material.